Near field communication or NFC technology is today widespread and can be embedded in any type of portable device. NFC components are produced which can be configured in a “reader”operating mode to read RFID tags (“Radio Frequency Identification tags”) or in a “card emulation”mode in which they emulate a contactless tag to exchange data with another reader.
Data is exchanged according to NFC technology by inductive coupling between an antenna coil of a reader and an antenna coil of the tag, through an alternating magnetic field transmitted by the reader, which generally oscillates at the standardized frequency of 13.56 kHz. Reader-type NFC components require large antenna coils, which represents a constraint for their integration into a mobile telephone.
Out of the various RFID tag technologies, there is a technique similar to the NFC technique, based on the principle of the electrical coupling of two UHF (“Ultra High Frequency”) antennas instead of being based on the inductive coupling of two RF antenna coils. This technique is used to read or write data in RFID tags referred to as “UHF tags.” UHF tags have a structure similar to that of NFC tags, but use a UHF antenna that is smaller than an NFC antenna coil. Like NFC tags, they generally transmit data passively using a backscattering technique involving modulating the reflection coefficient of the UHF tag antenna. Finally, like NFC tags, UHF tags can be purely passive and electrically powered by the electrical field emitted by the reader.
The cost price of UHF tags is lower than that of NFC tags. For the same features (mainly the memory size), their cost price is generally two to three times lower. This is mainly due to the fact that the surface area and the thickness of the antenna are reduced, thus decreasing the raw material requirements and enabling less expensive manufacturing processes to be used and increasing the rate of production lines.
There has been some desire for the two contactless communication techniques, NFC and UHF, to coexist. For example, the application International Patent Publication No. WO 2004/034317 or U.S. Patent Application Publication No. 2005/0186904 describes an NFC-UHF tag. The application International Patent Publication No. WO 2010/015753 describes an NFC/UHF converter enabling an NFC reader to be used to read UHF tags.
Regarding UHF tag readers, the emission of an electric field in the UHF band (860 MHz-960 MHz) also enables smaller antennas to be used which are thus easier to integrate into small devices such as mobile telephones. As an example, the company TagSense sells a small UHF reader under the name “NANO-UHF RFID READER,” particularly designed to be integrated into a mobile telephone. This “nano-reader” operates both at the European UHF frequencies (865-868 MHz) and the North-American UHF frequencies (902-928 MHz). The nano-reader includes an oscillator, a controller, a modulator and a demodulator. The backscattering signal is demodulated up to the baseband through an I/Q mixing stage and is then filtered and amplified. The demodulated signal is then sampled and processed by the controller. The nano-reader is connected to a host processor through a three-wire bus.
FIG. 1 schematically shows a mobile telephone HD0 equipped with a UHF tag reader RT0. The telephone HD0 includes a baseband processor BBP, a clock generator CKG and a transceiver TR0. The transceiver TR0 is connected to a first antenna A1 and the reader RT0 is connected to a second antenna A2. The processor BBP is linked to the transceiver TR0 through a control bus CTB and to the reader RT0 through a data bus DTU. It controls the clock generator CKG by way of an on/off signal CKON.
The processor BBP thus uses firstly the transceiver TR0 to establish a connection to a base station BST of the GSM network, through the antenna A1, and secondly the UHF reader RT0 to read and/or write data in a UHF tag TG, through the antenna A2.
Although it is less complicated than integrating an NFC reader, integrating a UHF reader into a mobile telephone is quite expensive. It may therefore be desirable to rationalize this integration to further reduce the cost price of a UHF reader.